Recent rotating electric machines suffer from increasing vibration applied to stator coils and heat generation by the stator coils due to higher power.
To suppress vibration of the stator coils in slots in a stator core, it is known to apply varnish (such as epoxy varnish) having a high strength (including a high bond strength and a high heat resistance) between the stator core and the stator coils for impregnation and adhesion. This creates, however, another problem that coating on enameled wires is peeled off due to thermal expansion and thermal shrinkage of the varnish associated with heat cycles and heat shock at coil ends outside of the stator core.
Thus, if a flexible unsaturated polyester varnish having a lower bond strength is used, peel off of the enamel coating can be prevented. However, the adhesion force between the slots in the stator core and the stator coils becomes insufficient and the coils are vibrated.
As described above, it is difficult to provide stator coils of the rotating electric machines with both strength and insulation.
A known example of a method of impregnating coil ends of a rotating electric machine with varnish includes coating the coil ends with chemical protected (CP) resin produced by synthesizing epoxy varnish, and coating the inside and the outside of the stator core with the epoxy varnish, so that external media do not enter the stator coil (for example, see PTL 1). Furthermore, another known method includes impregnating a stator core with epoxy varnish and molding the coil ends with epoxy varnish mixed with a filler (for example, see PTL 2).